The overall objective of this research is to elucidate the nature and organization of conceptual knowledge in early childhood and to determine how that mental structure is reflected in information processing. Several studies focus on the comprehension of and memory for lexical elements and connected discourse, and others on the nature of conceptual categories. One line of investigation concerns the organization of children's concepts of objects, actions, and relations as reflected in processes involving words which designate those concepts. A series of experiments has been completed and others are in progress. Memory is better for related than for unrelated nouns even in 3 year olds. Effects are less marked for verbs at all ages with fast presentation and at all rates for small children. It was concluded that nouns form stronger domains than verbs, that the structural organization is established in early childhood, but that information processing changes with age. One study in progress systematically explores the effects of semantic organization on naming latency. The design controls for effects of expectation and investigates the temporal parameters of semantic relatedness effects across age. A second ongoing study involves a longitudinal investigation of sentence comprehension in prelinguistic children which focuses on the understanding of verbs and the sentences involving those verbs. A third investigation is a non-verbal categorization study which examines the development of object, action, and relation categories in children 18 months to 3 years using a simple matching task. These non-verbal tasks will be used to compare conceptual development to the development of the comprehension and production of words for these categories.